Control device for head unit having optical head and multiple magnetic heads

ABSTRACT

A head unit control device having an optical head unit for radiating a laser beam onto a magneto-optical disc, and a magnetic head unit including a floating magnetic head and a fixed magnetic head. Luminous flux is radiated onto the magnet head unit and the optical head unit. The luminous flux reflected by these units is sensed by photo detectors, so that a relative position error signal is generated by a sensing circuit. When information is overwritten onto the magneto-optical disc on which information has already been previously recorded, the floating magnetic head is moved synchronously with the optical head, based on the relative position error signal. When information is recorded on the magneto-optical disc on which information has not been previously recorded, the fixed magnetic head is moved synchronously with the optical head, based on the relative position error signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for controlling head unitsprovided in a magneto-optical recording-reproduction device by whichinformation is recorded on a magneto-optical disc, information recordedon the magneto-optical disc being reproduced, or being erased from the.magneto-optical disc

2. Description of the Related Art

In a magneto-optical disc used in a magneto-opticalrecording-reproduction device, a 5.25 inch double side typemagneto-optical disc is known in which information can be recorded ontwo surfaces of the disc, the information recorded on the two surfacescan be erased, and can be reproduced, according to ISO (InternationalOrganization for Standardization) standards.: The erasing, recording andreproducing operations on the magneto-optical disc are carried out by amagneto-optical recording-reproduction device having a fixed magnetichead generating a bias magnetic field, and an optical head.

In this kind of magneto-optical disc, a known method of recording,reproduction and erasing of information on a magneto-optical disc can becarried out by magnetic field modulation. According to a recordingoperation by the magnetic field modulation method, new information canbe easily overwritten on a track on which old information has beenstored. The magneto-optical recording-reproduction device, which canoverwrite information on the magneto-optical disc, has an optical headfor radiating a laser beam onto the magneto-optical disc to recordinformation on the magneto-optical disc and reproduce the information,and a fixed magnetic head imposing a modulated magnetic field of themagneto-optical disc to overwrite information on the magneto-opticaldisc.

When reproducing information stored on the magneto-optical disc, themagneto-optical recording-reproduction device radiates a laser beam ontothe magneto-optical disc from the optical head, and receives the beamreflected from the magneto-optical disc by a photo detector. Whenoverwriting information on the magneto-optical disc, the magneto-opticalrecording-reproduction device imparts a modulated magnetic field forrecording the information, onto a point of the magneto-optical disc ontowhich the laser beam is also radiated from the optical head.

In the magneto-optical recording-reproduction device using the magneticfield modulation method, there is a device in which a floating magnetichead is provided as the magnetic head. By using this floating magnetichead, information can be recorded on the magneto-optical disc with highdensity.

The magneto-optical disc used in the magneto-opticalrecording-reproduction device having the floating magnetic head is asingle sided type magneto-optical disc on which information can beoverwritten only on one surface of the disc, which is different from thedouble side type magneto-optical disc for which the fixed magnetic headis used. This is due to a construction in which the floating magnetichead needs to be brought close to the magneto-optical disc.

Accordingly, even when the double sided type magneto-optical disc ismounted in the magneto-optical recording-reproduction device in whichthe floating magnetic head is provided, information cannot be recordedon the double sided type magneto-optical disc.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a head unitcontrol device by which information can be overwritten onto a singlesided type magneto-optical disc, and information can be recorded on adouble sided type magneto-optical disc.

According to the present invention, a head unit control device isprovided in a magneto-optical record device, comprising an optical headunit, a magnetic head unit, a radiating mechanism, and a controlmechanism.

The optical head unit radiates a laser beam onto a magneto-optical disc,and moves relative to the magneto-optical disc. The magnetic head unitmoves in synchronously with the optical head units and has a firstmagnetic head and a second magnetic head. The radiating mechanismradiates a luminous flux to the optical head unit and the magnetic headunit. The luminous flux is reflected by the optical head unit and themagnetic head unit. The control mechanism controls the optical head unitand the magnetic head unit based on the luminous flux reflected from theoptical head unit and the magnetic head unit, whereby one of the firstand second magnetic heads is moved while maintaining a predeterminedpositional relationship with the optical head unit.

Further, according to the .present invention, there is provided amagneto-optical record device, comprising an optical head unit, amagnetic head unity a radiating unit, reflecting portions, and a sensingunit.

The optical head unit radiates a laser beam onto a magneto-optical disc.The magnetic head unit moves in synchronously with the optical headunit, and includes a plurality of magnetic heads which have functionsthat differ from each other. The radiating unit is provided forradiating luminous flux onto the optical head unit and the magnetic headunit to sense positions of the optical head unit and the magnetic headunit. The reflecting portions are provided on the optical head unit andthe magnetic head unit to reflect the luminous flux radiated from theradiating unit. The sensing unit generates a relative position errorsignal, based on a reflected luminous flux from the optical head unitand the magnetic head unit, so that each of the magnetic heads is movedin synchronously with the optical head unit, when information isrecorded on the magneto-optical disc by each of the magnetic heads.

Furthermore, according to the present inventions a head unit controldevice is provided in a magneto-optical recording device, comprising anoptical head unit, a magnetic head unit, a radiating mechanism, agenerating mechanism, and a control mechanism.

The optical head unit radiates a laser beam onto a magneto-optical disc,and moves in a direction of the magneto-optical disc. The magnetic headunit moves in a direction of the magneto-optical disc and insynchronization with the optical head unit so as to be positioned at thesame relative position where the optical head unit is located. Themagnetic head unit has a floating magnetic head and a fixed magnetichead. The radiating mechanism radiates a luminous flux to the opticalhead unit and the magnetic head unit. The generating mechanism generatesa relative position error signal, based on a reflected luminous fluxfrom the optical head unit and the magnetic head unit. The controlmechanism controls the optical head unit and the magnetic head unitbased on the relative postional error signal, whereby one of thefloating magnetic head and the fixed magnetic head is moved to maintaina constant positional relationship with the optical head unit.

Further, according to the present invention, there is provided a devicefor selecting a magnetic head to be operated together with an opticalhead to record or reproduce a signal on a magneto-optical disc,comprising a first magnetic head and a second magnetic head, a carriage,a determining mechanism, and a control mechanism.

The first magnetic head and the second magnetic head have differentfunctions from each ,others and are arranged along the radial directionof the magneto-optical disc. The carriage is movable along the radialdirection of the magneto-optical discs and carries the first and secondmagnetic heads. The determining mechanism determines which type ofmagneto-optical disc is in use. The control mechanism controls theposition of the carriage based on the type of magneto-optical discdetermined by the determining mechanism, whereby the position of thecarriage is controlled so that the first or second magnetic head facesthe optical: head.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the description ofthe preferred embodiments of the invention set forth below, togetherwith the accompanying drawings, in which:

FIG. 1 is a perpendicular view showing a first embodiment in a state inwhich an overwriting operation is carried out by an optical head and afloating magnetic head;

FIG. 2 is a perpendicular view showing the first embodiment in a statein which a recording operation is carried out by the optical head and afixed magnetic head;

FIG. 3 is a diagram showing the characteristics of an optical head photodetector and a magnetic head photo detector;

FIG. 4 is a perspective view showing the optical head photo detector;

FIG. 5A is a sectional view showing a state in which a floating magnetichead and an optical head unit are located at the innermost position of amagneto-optical disc;

FIG. 5B is a sectional view showing a state in which the floatingmagnetic head and the optical head unit are located at the outermostposition of a magneto-optical disc;

FIG. 6 is a view showing a change of luminous flux reflected by amagnetic head reflecting mirror when a magnetic head carriage is moved;

FIG. 7A is a sectional view showing a state in which a fixed magnetichead and an optical head unit are located at the innermost position of amagneto-optical disc;

FIG. 7B is a sectional view showing a state in which the fixed magnetichead and the optical head unit are located at the outermost position ofa magneto-optical disc;

FIG. 8 is a block diagram showing a magneto-opticalrecording-reproduction device in which position control of a magnetichead unit according to a first example is carried out;

FIG. 9 is a flowchart showing an operation of a control unit in thefirst example;

FIG. 10 is a flowchart showing an operation of a sensing circuit in thefirst example;

FIG. 11 is a block diagram showing a magneto-opticalrecording-reproduction device in which a position control of a magnetichead unit according to a second example is carried out;

FIG. 12 is a sectional view showing an optical switch;

FIG. 13 is a flowchart showing an operation of a sensing circuit in thesecond example;

FIG. 14 is a block diagram showing a magneto-opticalrecording-reproduction device in which a position control of a magnetichead unit according to a third example is carried out;

FIG. 15 is a flowchart showing an operation of a sensing circuit in thethird example;

FIG. 16 is a perpendicular view showing a second embodiment in a statein which an overwriting operation is carried out by an optical head anda floating magnetic head;

FIG. 17 is a view showing a sensing operation in the second embodimentin which a position of an optical head carriage is sensed;

FIG. 18 is a view showing a sensing operation in the second embodimentin which a position of a magnetic head carriage is sensed;

FIG. 19 is a block diagram showing the magneto-opticalrecording-reproduction device in which a position control of themagnetic head unit according to a first example in the second embodimentis carried out;

FIG. 20 is a flowchart showing an operation of a sensing circuit in thefirst example;

FIG. 21 is a block diagram showing a magneto-opticalrecording-reproduction device in which a position control of a magnetichead unit according to a second example of the second embodiment iscarried out;

FIG. 22 is a flowchart showing an operation of a sensing circuit in thesecond example;

FIG. 23 is a block diagram showing a magneto-opticalrecording-reproduction device in which a position control of a magnetichead unit according to a third example of the second embodiment iscarried out; and

FIG. 24 is a flowchart showing an operation of a sensing circuit in thethird example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference toembodiments shown in the drawings.

FIGS. 1 and 2 show a first embodiment of a magneto-opticalrecording-reproduction device according to the present invention. Inthis device, a magneto-optical disc M housed in a cartridge case (notshown) is used. The magneto-optical disc M may be a 5.25 inch diametersingle sided type magneto-optical disc, or a 5.25 inch diameter doublesided type magneto-optical disc.

The magneto-optical recording-reproduction device is provided with aspindle motor 10 for rotating the magneto-optical disc M.

Linear motors 20, 20 and an optical head unit 30 are provided at oneside of the magneto-optical disc M, and a magnetic head unit 40 isprovided at the other side of the magneto-optical disc M. Namely, themagnetic head unit 40 is disposed at a position opposite to the opticalhead unit 30 about the magneto-optical disc M. The optical head unit 30and the magnetic head unit 40 are movable relative to themagneto-optical disc M.

The linear motors 20, 20 have linear motor magnets 21, 21, which aredisposed separately from each other in such a manner that thelongitudinal direction of each of the linear motor magnets 21, 21 isparallel to the radial directions A1, A2 of the magneto-optical disc M.The linear motors 20, 20 have optical head moving coils 22, 22, whichare provided on the linear motor magnets 21, 21 to be movable in theradial directions A1, A2. The optical head moving coils 22, 22 are movedin the radial directions A1, A2 when electric current is appliedthereto.

The optical head unit 30 has an optical head carriage 31 providedbetween the optical head moving coils 22, 22. The optical head unit 30has an optical head 32, which is held on the optical head carriage 31.The optical head 32 is moved in the radial directions A1, A2 of themagneto-optical disc M by the linear motors 20, 20, and gains access toa target track of the magneto-optical disc hi by an operation of acontrol unit 15. The optical head 32 radiates a laser beam onto themagneto-optical disc M through an objective lens 33, when recordinginformation MO on the magneto-optical disc M, and when reproducinginformation from the magneto-optical disc M. The optical head 32 has aphoto detector (not shown) for receiving a laser beam reflected from themagneto-optical disc M to sense the information stored on themagneto-optical disc M when reproducing the information.

The magnetic head unit 40 has a magnetic head carriage 41, which isprovided between coils of linear motors (not shown), similarly to theoptical head carriage 31. The magnetic head carriage 41 is moved in theradial directions A1, A2 of the magneto-optical disc M, issynchronization with the optical head carriage 31 by an operation of acontrol unit 15.

The magnetic head carriage 41 has a floating magnetic head 42 and afixed magnetic head 43 each of which has a different functions from theother, as described hereafter. The floating magnetic head 42 and thefixed magnetic head 43 face the surface of the magneto-optical disc M,and are aligned in the radial direction A1 separated from each other bya distance L1. In other words, the floating magnetic head 42 and thefixed magnetic head 43 are aligned in the direction in which themagnetic heads 42, 43 are moved.

The floating magnetic head 42 is held on the magnetic head carriage 41to be movable in a direction B perpendicular to the surface of themagneto-optical disc Ms so that the floating magnetic head 42 approachesor moves away from the magneto-optical disc M. The floating magneticdisc 42 floats slightly above the surface of the magneto-optical disc Mdue to an air flow generated by the rotation of the magneto-optical discM, when the floating magnetic head 42 approaches the magneto-opticaldisc M. Then, the floating magnetic head 42 applies a modulated magneticfield onto a portion of the magneto-optical disc M which corresponds toa portion where a laser beam outputted from the optical head 32 isradiated, so that information is overwritten on the magneto-optical discM with high density. This floating magnetic head 42 is used for a 5.25inch diameter single side type disc which is constructed in such amanner that information can be overwritten on one surface of the disc.In the overwriting operation, the floating magnetic head 42 is locatedat a position corresponding to a position at which the objective lens 33of the optical head 32 is located, as shown in FIG. 1.

The fixed magnetic head 43 is fixed on the magnetic head carriage 41, sothat the fixed magnetic head 43 applies a bias magnetic field to themagneto-optical disc M to record information thereon. The fixed magnetichead 43 is used for a 5.25 inch diameter double sided type disc which isconstructed in such a manner that information can be recorded aftererasing information which has been recorded on the disc. In thisrecording operations the fixed magnetic head 43 is located at a positioncorresponding to a position at which the objective lens 33 of theoptical head 32 is located, as shown in FIG. 2.

An optical system and a sensing system, which are provided for movingthe floating magnetic head 42 and the fixed magnetic head 43 insynchronization with the optical head 32, are described below.

A light source 51 radiates a luminous flux in a direction perpendicularto a side face 31A of the optical head carriage 31, i.e., in the radialdirection A1. The light source 51 has a radiating portion whichgenerates a laser beam, and a lens which converts the laser beamradiated from the radiating portion into a parallel beam, the radiatingportion and the lens not being shown.

A beam splitter 52 splits the luminous flux outputted from the lightsource 51 into a luminous flux advancing in a straight direction and aluminous flux advancing in a direction perpendicular to the straightdirection, and radiates the luminous flux advancing in the straightdirection onto the side face 31A of the optical head carriage 31.

An optical head reflecting mirror 34 is attached to the side face 31A ofthe optical head carriage 31. The luminous flux advancing in thestraight direction from the beam splitter 52 enters the optical headreflecting mirror 34. The mirror plane of the optical head reflectingmirror 34 is inclined by an angle α/2 with respect to a faceperpendicular to the luminous flux entering the mirror, so that theoptical head reflecting mirror 34 reflects the luminous flux at an angleα.

An optical head photo detector 61 receives the luminous flux which isreflected by the optical head reflecting mirror 34 and is converged by acondenser lens 53, and senses a central position of the distribution ofthe luminous flux received by the optical head photo detector 61.Namely, the optical head photo detector 61 is a PSD (Position SensitiveDevice) which senses the position of the luminous flux entering a beamreceiving face 61A of the optical head photo detector 61. The beamreceiving face 61A is inclined by an angle α/2 with respect to themirror plane of the optical head reflecting mirror 34.

The characteristics of the optical head photo detector 61 form anS-shaped curve as shown in FIG. 3. Namely, when the luminous fluxpassing through the condenser lens 53 is moved in the longitudinaldirection C of the beam receiving face 61A and enters into the condenserlens 53 as the luminous flux 101, as shown in FIG. 4, an output PSD1 ofthe optical head photo detector 61 becomes a minus value as shown inFIG. 3. When the luminous flux passing through the condenser lens 53enters into the center of the beam receiving face 61A as the luminousflux 102, as shown in FIG. 4, the output PSD1 becomes Zero as shown inFIG. 3. When the luminous flux passing through the condenser lens 53 ismoved in the opposite direction of the direction C and enters into thecondenser lens 53 as the luminous flux 103, as shown in FIG. 4, theoutput PSD1 becomes a positive value, as shown in FIG. 3. Thus, theoptical head photo detector 61 generates the output PSD1 correspondingto the position of the luminous flux entering to the beam receiving face61A.

Note, in the first embodiment, when the optical head 32 is positionednear the center of the magneto-optical disc M, the luminous fluxreflected by the optical head reflecting mirror 34 is moved in thedirection C, as the luminous flux 101 in FIG. 4. When the optical head32 is positioned in the middle of the recording portion of themagneto-optical disc M, the luminous flux enters the center of the beamreceiving face 61A of the optical head photo detector 61 as the luminousflux 102 in FIG. 4. When the optical head 32 is positioned near the edgeof the magneto-optical disc M, the luminous flux is moved in theopposite direction of the direction C as the luminous flux 103 in FIG.4.

A rectangular prism 54 reflects the luminous flux reflected by the beamsplitter 52 to a side face 41B of the magnetic head carriage 41.

A magnetic head reflecting mirror 44 is fixed on the side face 41A ofthe magnetic head carriage 41, similarly to the optical head reflectingmirror 34. The mirror plane of the optical head reflecting mirror 34 isinclined so that the luminous flux reflected from the rectangular prism54 is reflected by an angle α.

A magnetic head photo detector 62 receives the luminous flux which isreflected by the magnetic head reflecting mirror 44 and is converged bya condenser lens 55, and senses a position of the luminous flux receivedby the optical head photo detector 62. Namely, the magnetic head photodetector 62 is also a PSD (Position Sensitive Device) as is the opticalhead photo detector 61. The beam receiving face 62A of the magnetic headphoto detector 62 is parallel to the beam receiving face 61A of theoptical head photo detector 61. The magnetic head photo detector 62generates an output PSD2 which is a signal similar to that outputted bythe optical head photo detector 61. Namely, the characteristics of themagnetic head photo detector 62 are the same as those of the opticalhead photo detector 61 shown in FIG. 3.

Note, in the first embodiment, when the floating magnetic head 42 ispositioned in the middle between the outermost and the innermost tracksof the magneto-optical disc M, the luminous flux reflected from themagnetic head reflecting mirror 44 enters the center portion of the beamreceiving face 62A of the magnetic head photo detector 62, similarly tothe luminous flux 102 shown in FIG. 4.

A sensing circuit 63 obtains a relative position error signal E based onthe difference between the output PSD1 of the optical head photodetector 61 and the output PSD2 of the magnetic head photo detector 62.The relative position error signal E indicates a positional relationshipbetween the magnetic head unit 40 and the optical head unit 30. Thesensing circuit 63 generates the relative position error signal E asfollows.

A case in which a single side type magneto-optical disc is used as themagneto-optical disc M and information is overwritten onto the singlesided type magneto-optical disc which has been previously recorded upon,is described below.

The sensing circuit 63 generates the relative position error signal Ewhich is zero when the floating magnetic head 42 is located at the samerelative position as the optical head 32 (the optimum position), and thesensing circuit 63 generates the relative position error signal E whichis not zero when the floating magnetic head 42 is not located at thesame relative position as the optical head 32.

If the position of the floating magnetic head 42 is offset from theoptical head 32, the relative position error signal E comes to have apositive value or a negative value. The control unit 15 controls amovement of the floating magnetic head 42, based on the relativeposition error signal E, in such a manner that the floating magnetichead 42 moves in synchronously with the optical head 32. As a result,the floating magnetic head 42 is moved from the innermost position ofthe magnetos-optical disc M which is shown in FIG. 5A to the outermostposition of the magneto-optical disc M which is shown in FIG. 5B, sothat the floating magnetic head 42 is moved while maintaining apredetermined positional relationship with the optical head 32, i.e., atthe same relative position as the optical head 32.

A case in which a double sided type magneto-optical disc is used as themagneto-optical disc M and information is recorded on the double sidedtype magneto-optical disc is described below.

The output PSD1 corresponding to a position of the optical head unit 30is zero when the optical head 32 is located at the radial middle portionof the magneto-optical disc M.

On the other hand, the control unit 15 controls the fixed magnetic head43 to move in the radial direction A1 so that the fixed magnetic head 43faces the optical head 32. When the fixed magnetic head 43 faces theoptical head 32, the output PSD2 outputted from the magnetic head photodetector 62 has a negative value. This is because the magnetic headphoto detector 62 is disposed in such a manner that, when the floatingmagnetic head 42 faces the optical head 32, the magnetic head photodetector 62 generates the output PSD2 which is zero. Therefore, as shownin FIG. 6, when the fixed magnetic head 43 is moved in the direction A1to face the optical head 32, and thus the luminous flux reflected by themagnetic head reflecting mirror 44 is moved in the direction C, themagnetic head photo detector 62 generates the output PSD2 having apredetermined negative value.

At this time, the sensing circuit 63 adds a predetermined offset valuecorresponding to the distance L1 to the output PSD2 outputted by themagnetic head photo detector 62, so that the output PSD2 becomes zero,whereby the relative position error signal E is adjusted to zero.

The control unit 15 controls the fixed magnetic head 43, based on therelative position error signal E which has been adjusted to zero byadding the offset, so that the fixed magnetic head 43 moves insynchronously with the optical head 32. As a result, the fixed magnetichead 43 is moved from the innermost position of the magneto-optical discM which is shown in FIG. 7A, to the outermost position of themagneto-optical disc M which is shown in FIG. 7B, so that the fixedmagnetic head 43 is moved while maintaining a predetermined positionalrelationship with the optical head 32, i.e., at the same relativeposition as the optical head 32.

Note, in the first embodiment, the light source 51, the beam splitter52, the condenser lenses 53, 55, and the rectangular prism 54 form aradiating mechanism which radiates luminous flux to the optical headunit 30 and the magnetic head unit 40. The optical head photo detector61, the magnetic head photo detector 62, and the sensing circuit 63 forma sensing mechanism which generates the relative position error signal.

With reference to FIGS. 8 through 15, examples of constructions forsensing the kind of magneto-optical disc M and controlling the positionof the magnetic head carriage 41 in the first embodiment are describedbelow.

FIG. 8 is a block diagram showing the magneto-opticalrecording-reproduction device in which a position control of themagnetic head unit 40 according to a first example is carried out.Regarding FIG. 8, only components which have not been described aboveare described below. A magnetic head drive circuit 49 and an opticalhead drive circuit 39 are controlled by the control unit 15 to move themagnetic head carriage 41 and the optical head carriage 31 in the radialdirection of the magneto-optical disc his respectively. An error signalsensing circuit 38 is provided for sensing a focusing error signal FEand a tracking error signal TE according to a known process, to outputthe signals FE and TE into the control unit 15, so that the position ofthe objective lens 33 is controlled. A recording signal sensing circuit37 senses information MO recorded on the magneto-optical disc hi throughthe optical head 32, and outputs the information MO into the controlunit 15.

As described later, the control unit 15 detects disc information DI, andoutputs the disc information DI to the sensing circuit 63, which obtainsthe relative position error signal E in accordance with the discinformation DI. The sensing circuit 63 outputs the relative positionerror signal E to the control unit 15, so that the position of themagnetic head carriage 41 is controlled.

FIG. 9 is a flowchart showing an operation of the control unit 15 in thefirst example, in which information indicating whether themagneto-optical disc M is a single sided type magneto-optical disc or adouble sided type magneto-optical disc is recorded in an SFP (StandardFormat Part) of a control track which is located at the innermost or theoutermost portion of the magneto-optical disc M.

In Step 101, the optical head 32 is moved and positioned at the controltrack of the magneto-optical disc M. Then, in Step 102, the informationMO recorded in the SPF of the control track is reproduced by therecording signal sensing circuit 37 to read the disc information DI, sothat it is determined whether the magneto-optical disc M is a singlesided type magneto-optical disc or double sided type magneto-opticaldisc. In Step 103, the disc information DI is outputted to the sensingcircuit 63, and the process is ended.

FIG. 10 is a flowchart showing an operation of the sensing circuit 63 inthe first example.

In Step 201, the disc information DI inputted from the control unit 15is read. In Step 202, it is determined whether or not themagneto-optical recording-reproduction device is being operated, namely,whether or not the spindle motor 10 is being rotated, for example. Whenthe magneto-optical recording-reproduction device is being operated, theprocess goes to Step 203 to control the magnetic head unit 40.Conversely, when the magneto-optical recording-reproduction device isnot being operated, the process is ended.

In Step 203, it is determined whether or not the magneto-optical disc Mis a single sided type magneto-optical disc on which information can beoverwritten. When the magneto-optical disc M is not a single sided typemagneto-optical disc, namely, when the magneto-optical disc M is adouble sided type magneto-optical disc, a predetermined offset valuecorresponding to the distance L1 is added to the output PSD2 outputtedby the magnetic head photo detector 62. Conversely, when themagneto-optical disc M is a single sided type magneto-optical disc, Step204 is skipped, and thus the process goes to Step 205, in which therelative position error signal E is controlled to be zero. The zerosignal E is outputted to the control unit 15, whereby the the floatingmagnetic head 42 or the fixed magnetic head 43 is moved in synchronouslywith the optical head 32.

FIG. 11 is a block diagram showing the magneto-opticalrecording-reproduction device in which a position control of themagnetic head unit 40 according to a second example is carried out. Inthe second example, as shown in FIG. 12, the magneto-opticalrecording-reproduction device has an optical switch or photo interrupter81. A cartridge 82 in which the magneto-optical disc M of the singlesided type magneto-optical disc is housed is provided with a hole 83,which is detected by the optical switch 81. Namely, when a lightradiated by a light emitting diode 81a is sensed by a photocell 81b, theoptical switch 81 is turned ON to output a signal indicating themagneto-optical disc M is a single sided type magneto-optical disc, andwhen a light radiated by the light emitting diode 81a is interrupted bythe cartridge 82, the optical switch 81 is turned OFF.

FIG. 13 is a flowchart showing an operation of the sensing circuit 63 inthe second example.

In Step 301, it is determined whether or not the magneto-opticalrecording-reproduction device is being operated, similarly to Step 202of FIG. 10. When the magneto-optical recording-reproduction device isbeing operated, the process goes to Step 302 to control the magnetichead unit 40, and when the magneto-optical recording-reproduction deviceis not being :operated, the process is ended.

In Step 302, it is determined whether the optical switch 81 is turned ONor OFF. When the optical switch 81 is turned OFF which means that themagneto-optical disc M is a double sided type magneto-optical discs apredetermined offset value corresponding to the distance L1 is added tothe output PSD2 in Step 303. Conversely, when the optical switch 81 isturned ON which means that the magneto-optical disc M is a single sidedtype magneto-optical disc, Step 303 is skipped, and thus the processgoes to Step 304 in which the same operation as Step 205 of FIG. 10 iscarried out.

FIG. 14 is a block diagram showing the magneto-opticalrecording-reproduction device in which a position control of themagnetic head unit 40 according to a third example is carried out. Inthe third examples the magneto-optical recording-reproduction device hasa select switch 85, which is operated by a user of the magneto-opticalrecording-reproduction device. The switch 85 is open when themagneto-optical disc M is a single side-type magneto-optical disc, andis closed when the magneto-optical disc M is a double sided typemagneto-optical disc.

FIG. 15 is a flowchart showing an operation of the sensing circuit 63 inthe third example.

Steps 401 through 404 correspond to Steps 301 through 304 of FIG. 13,and only Step 402 is different from Step 302. Namely, in Step 402, it isdetermined whether the select switch 85 is open or closed. When theoptical switch 85 is closed which means that the magneto-optical disc Mis a double sided type magneto-optical disc, a predetermined offsetvalue corresponding to the distance L1 is added to the output PSD2 inStep 403. Conversely, when the select switch 85 is closed which meansthat the magneto-optical disc M is a single sided type magneto-opticaldisc, Step 403 is skipped, and thus the process goes to Step 404 inwhich the same operation as Step 205 of FIG. 10 is carried out.

Thus, according to the first embodiment, information can be overwrittenonto a 5.25 inch diameter single sided type magneto-optical disc usingthe magnetic field modulation method. Further, information can berecorded on a double sided type magneto-optical discs and informationstored on a double sided type magneto-optical disc can be erased.

FIG. 16 shows a second embodiment of the magneto-opticalrecord-reproduction device according to the present invention. In thisdevice, a first light source 71, a second light source 72, and a thirdlight source 73 are provided as the radiating mechanism, and of thefirst embodiment. Note, in the second embodiment, the same a sensingcircuit 64 is provided instead of the sensing circuit 63 referencenumerals are applied to the same or corresponding portions as in thefirst embodiment, and descriptions of these portions are omitted.

The first light source 71 radiates luminous flux onto the optical headreflecting mirror 34 of the optical head carriage 31, by an angle α withrespect to the radial direction A1. The light source 71 has a radiatingportion which generates a laser beam and a lens which converts the laserbeam radiated from the radiating portion into a parallel beam; theradiating portion and the lens are not shown.

The luminous flux outputted from the light source 71 is reflected by theoptical head .reflecting mirror 34 to advance in the radial directionA2, and is converged by the condenser lens 53, to enter into the opticalhead photo detector 61. When the optical head carriage 31 is moved inthe radial direction A1, for example, the position at which the luminousflux enters into the optical head reflecting mirror 34 is moved in thedirection D perpendicular to the radial direction A1, as shown in FIG.17. In accordance with this movement, the optical head photo detector 61generates an output PSD1, similarly to the first embodiment.

The second light source 72 and the third light source 73 have a similarconstruction to the first light source 71. The second light source 72radiates a luminous flux onto the magnetic head reflecting mirror 44 ofthe magnetic head carriage 41 by an angle α with respect to the radialdirection A1, to sense a position of the floating magnetic head 42. Thethird light source 73 radiates a luminous flux onto the magnetic headreflecting mirror 44 in parallel to the luminous flux of the secondlight source 72, to sense a position of the fixed magnetic head 43. Thesecond light source 72 and the third light source 73 are disposed atdifferent positions along the radial direction of the disc M, by anamount corresponding to the distance L1.

When information is overwritten onto a single sided type magneto-opticaldisc which has been recorded on, luminous flux outputted by the secondlight source 72 is radiated to the magnetic head reflecting mirror 44,as shown in FIG. 18. This luminous flux is reflected by the magnetichead reflecting mirror 44 in the radial direction A2, and converged bythe condenser lens 55 to enter into the magnetic head photo detector 62,which generates an output PSD2, similarly to the first embodiment.

The sensing circuit 64 obtains a relative position error signal E basedon the difference between the output PSD1 of the optical head photodetector 61 and the output PSD2 of the magnetic head photo detector 62.The relative position error signal E is outputted to the control unit 15so that the floating magnetic head 42 is moved in synchronously with theoptical head 32.

When information is recorded onto a double sided type magneto-opticaldisc, luminous flux outputted by the third light source 73 is radiatedto the magnetic head reflecting mirror 44. At this time, since theluminous flux entering into the magnetic head photo detector 62 isoffset from the center of the light receiving area of the magnetic headphoto detector 62, the magnetic head photo detector 62 generates anoutput PSD2 corresponding to the position at which the luminous fluxenters, and transmits the output PSD2 to the sensing circuit 64, bywhich the sensing circuit 64 outputs a relative position error signal Eto the control unit 15 based on the output PSD1 and the output PSD2. Thecontrol unit 15 controls the magnetic head carriage 41 to be moved inthe radial direction A1. Then, when the fixed magnetic head 43 comes toa position where the fixed magnetic head 43 faces the optical head 32,the relative position error signal E becomes zero. The sensing circuit64 then outputs the relative position error signal E (zero) so that thefixed magnetic head 43 is moved in synchronously with the optical head32.

Note, operations of the second and third light sources 72 and 73 areswitched by the sensing circuit 64.

FIGS. 19 through 24 show examples of constructions for sensing the kindof magneto-optical disc M and controlling the position of the magnetichead carriage 41 in the second embodiment.

FIG. 19 is a block diagram showing the magneto-opticalrecording-reproduction device in which a position control of themagnetic head unit 40 according to a first example is carried out. InFIG. 19, only the light sources 71, 72 and 73 are different from thelight source 51 in FIG. 8, and the other components are the same asthose in FIG. 8. Operation of the control unit 15 is also the same asthat of FIG. 9.

Regarding the operation of the sensing circuit 64, as shown in FIG. 20,when it is determined that the magneto-optical disc M is not a singlesided type magneto-optical disc, the third light source 73 is actuatedin Step 214, and when the magneto-optical disc M is a single sided typemagneto-optical disc, Step 214 is skipped, and thus the process goes toStep 205. The other Steps are the same as those shown in FIG. 10.

FIG. 21 is a block diagram showing the magneto-opticalrecording-reproduction device in which position control of the magnetichead unit 40 according to a second example is carried out. In the secondexample, the construction of the magneto-optical recording-reproductiondevice is the same as that shown in FIG. 11, except that the lightsources 71, 72 and 73 are provided.

In the operation of the sensing circuit 64, as shown in FIG. 22, when itis determined that the optical switch 81 is turned OFF, the third lightsource 73 is actuated in Step 313, and when the optical switch 81 isturned ON, Step 313 is skipped, and thus the process goes to Step 304.The other Steps are the same as those shown in FIG. 13.

FIG. 23 is a block diagram showing the magneto-opticalrecording-reproduction device in which position control of the magnetichead unit 40 according to a third example is carried out. In the thirdexample, the construction of the magneto-optical recording-reproductiondevice is the same as that shown in FIG. 14, except that the lightsources 71, 72 and 73 are provided.

In the operation of the sensing circuit 64, as shown in FIG. 24, when itis determined that the select switch 85 is turned OFF, the third lightsource 73 is actuated in Step 414, and when the select switch 85 isturned ON, Step 414 is skipped, and thus the process goes to Step 404.The other Steps are the same as those shown in FIG. 15.

Thus, according to the second embodiment, the sensing circuit 64 doesnot impose an offset on the output PSD2 of the magnetic head photodetector 62, but only obtains the difference between the output PSD1 andthe output PSD2. Therefore, the construction of the sensing circuit 64is simpler than the sensing circuit 63 of the first embodiment.

Although the embodiments of the present invention have been describedherein with reference to the accompanying drawings, obviously manymodifications and changes may be made by those skilled in this artwithout departing from the scope of the invention.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 4-86831 (filed on Apr. 8, 1992) which isexpressly incorporated herein by reference in its entirety.

I claim:
 1. A device for controlling head units provided in amagneto-optical recording device, comprising:an optical head unit forradiating a laser beam onto a magneto-optical disc, said optical headunit moving relative to said magneto-optical disc; a magnetic head unitsynchronously movable with said optical head unit, and having a firstmagnetic head and a second magnetic head; radiating means for radiatinga luminous flux to said optical head unit and said magnetic head unit,said luminous flux being reflected by said optical head unit and saidmagnetic head unit; and control means for controlling said optical headunit and said magnetic head unit based on said luminous flux reflectedfrom said optical head unit and said magnetic head unit, whereby one ofsaid first and second magnetic heads is moved while maintaining apredetermined positional relationship with respect to said optical headunit, wherein said control means comprises means for generating arelative position error signal indicating a positional relationshipbetween one of said first magnetic head and said second magnetic headwith respect to said optical head unit, and wherein said generatingmeans adds an offset to a signal obtained by said luminous fluxreflected from said magnetic head unit, when said second magnetic headis located at the same position as said optical head unit, whereby saidrelative position error signal is adjusted to zero.
 2. A deviceaccording to claim 1, wherein said magnetic head unit is disposed at aposition opposite to said optical head unit in relation to saidmagneto-optical disc.
 3. A device according to claim 1, wherein saidfirst magnetic head and said second magnetic head have differentfunctions from each other.
 4. A device according to claim 3, whereinsaid first magnetic head is a floating magnetic head provided forapplying a modulated magnetic field to a portion of said magneto-opticaldisc which corresponds to a portion where said laser beam is radiated bysaid optical head unit.
 5. A device according to claim 3, wherein saidsecond magnetic head is a fixed magnetic head for applying a biasmagnetic field to said magneto-optical disc to record informationthereon.
 6. A device according to claim 1, wherein said first magnetichead and said second magnetic head are aligned in a direction in whichsaid first and second magnetic heads are moved.
 7. A device according toclaim 1, wherein said optical head unit comprises a reflecting mirrorwhich reflects said luminous flux.
 8. A device according to claim 7,wherein said reflecting mirror has a mirror plane which is inclined by apredetermined angle with respect to a face perpendicular to saidluminous flux radiated by said radiating means.
 9. A device according toclaim 8, wherein said control means comprises a position sensitivedevice having a beam receiving portion which is inclined by saidpredetermined angle with respect to said mirror plane.
 10. A deviceaccording to claim 1, wherein said magnetic head unit comprises areflecting mirror which reflects said luminous flux.
 11. A deviceaccording to claim 10, wherein said reflecting mirror has a mirror planewhich is inclined by a predetermined angle with respect to a faceperpendicular to said luminous flux radiated by said radiating means.12. A device according to claim 1, wherein said control means controlssaid optical head unit and said magnetic head unit in such a manner thatone of said first and second magnetic heads and said optical head unitare positioned at the same position.
 13. A device according to claim 1,wherein said generating means generates said relative position errorsignal which is zero when said first magnetic head is located at thesame relative position as said optical head unit, and generates saidrelative position error signal which is not zero when said firstmagnetic head is not located at the same position as said optical headunit.
 14. A device according to claim 1, wherein said radiating meanscomprises one light source, and means for splitting said luminous fluxinto two directions to be directed to said optical head unit and saidmagnetic head unit, respectively.
 15. A device according to claim 1,wherein said control means has means for determining the type ofmagneto-optical disc, to control said optical head unit and saidmagnetic head unit in accordance with the said type of magneto-opticaldisc.
 16. A device according to claim 15, wherein said control meansdetermines the type of magneto-optical disc based on informationrecorded in a Standard Format Part of a control track of saidmagneto-optical disc.
 17. A magneto-optical recording device,comprising:an optical head unit radiating a laser beam onto amagneto-optical disc; a magnetic head unit synchronously movable withsaid optical head unit, and including a plurality of magnetic headshaving different functions from each other; a radiating unit providedfor radiating luminous flux to said optical head unit and said magnetichead unit to sense positions of said optical head unit and said magnetichead unit; reflecting portions provided on said optical head unit andsaid magnetic head unit to reflect said luminous flux radiated from saidradiating unit; a sensing unit generating a relative position errorsignal, based on a reflected luminous flux from said optical head unitand said magnetic head unit, so that each of said magnetic heads movessynchronously with said optical head unit, when information is recordedon said magneto-optical disc by said each of said magnetic heads; andmeans for generating a relative position error signal indicating apositional relationship between one of said plurality of magnetic headswith respect to said optical head unit, and wherein said means forgenerating adds an offset to a signal obtained by said luminous fluxreflected from said magnetic head unit, when one of said plurality ofmagnetic heads is located at the same position as said optical headunit, whereby said relative position error signal is adjusted to zero.18. A device for controlling head units provided in a magneto-opticalrecording device, comprising:an optical head unit radiating a laser beamonto a magneto-optical disc, said optical head unit moving in adirection of said magneto-optical disc; a magnetic head moving in adirection of said magneto-optical disc and in synchronization with saidoptical head unit to be positioned at the same relative position wheresaid optical head unit is located, said magnetic head unit having afloating magnetic head and a fixed magnetic head; means for radiatingluminous flux to said optical head unit and said magnetic head unit;means for generating a relative position error signal, based on areflected luminous flux from said optical head unit and said magnetichead unit and indicating a positional relationship between one of saidfloating magnetic head and said fixed magnetic head with respect to saidoptical head unit, and wherein said means for generating adds an offsetto a signal obtained by said luminous flux reflected from said magnetichead unit, when one of said floating magnetic head and said fixedmagnetic head is located at the same position as said optical head unit,whereby said relative position error signal is adjusted to zero; andmeans for controlling said optical head unit and said magnetic head unitbased on said relative position error signal, whereby one of saidfloating magnetic head and said fixed magnetic head is moved to maintainthe same relative position as said optical head unit.